Our investigations include: (1) a continuing study of the relationship of genetic recombination of DNA repair-defectiveness in strains of yeast selected for hypersensitivity to methyl methanesulfonate, (2) a study of genetic crossing-over and its correlation with gene conversion in mitotic cells, (3) the mapping of UGA nonsense suppressors, (4) the identification of a translocation involving chromosomes III and V and its effect on mating type, (5) a continuation of studies of genes modifying the behavior of cell division cycle mutants, and (6) the effect of carbon source on the expression of cell division cycle mutations.